1. Field of the Invention
This invention relates to a marine propulsion unit for a watercraft, and more particularly to a tilt and trim adjustment system for a marine propulsion unit.
2. Description of Related Art
Outboard motors with four-cycle engines have grown in popularity in recent years, due in part to environmental concerns associated with two-cycle outboard motors. The application of four-cycle engines in outboard motors, however, has raised some challenges, especially with large horse power engines. A four-cycle engine will weigh significantly more that a two-cycle engine that produces a comparable horsepower to that of the four-cycle engine. The additional weight creates problems for the conventional hydraulic power tilt and trim systems used with the outboard motor.
A hydraulic power tilt and trim system supports an outboard motor on a watercraft, and adjusts the trim and tilt position of the outboard motor. A tilt and trim adjustment mechanism of the system commonly includes at least one hydraulic actuator which operates between a clamping bracket and a swivel bracket. The clamping bracket is attached to the watercraft and the swivel bracket supports the outboard motor. A pivot pin connects together the swivel and clamping brackets. The actuator causes the swivel bracket to pivot about the axis of the pivot pin, relative to the stationary clamping bracket, to raise or lower the outboard drive.
Tilt and trim adjustment mechanisms also usually employ a powering unit that affects the trim and tilt operations of the outboard motor. For this purpose, powering units have included a reversible electric motor that selectively drives a reversible fluid pump. The pump pressurizes or depressurizes the actuator for raising or lowering the outboard motor.
In particular, the fluid pump supplies pressurized fluid to various ports of the actuator's closed cylinder, on either side of a piston which slides within the cylinder. The piston forms separate chambers within the cylinder. A conventional seal, such as one or more O-rings, operates between the piston and cylinder bore to prevent flow from between the chambers. The piston moves within the cylinder by pressurizing the chamber on one side of the piston and depressurizing the other chamber on the opposite side.
An actuator arm is attached to the piston and to the swivel bracket. The other end of the cylinder is attached to the clamping bracket. By pressurizing and depressurizing the chambers within the actuator, the piston and thus the outboard motor can be moved.
The actuator and powering unit often are located adjacent to each other in a side-by-side relationship, as illustrated in U.S. Pat. No. 5,049,099. The powering assembly formed by the pump, reservoir and motor, extends along side the actuator for most of the actuator's length. Both the actuator and the powering unit lie between bracket arms of the clamping and swivel brackets. While these components are shielded in this position, the resulting assembly off sets the actuator from the center of gravity of the outboard motor. That is, the stroke axis of the actuator and the center of gravity of the outboard motor which it moves, are not within the same plane. Consequently more force is required to raise the outboard motor, which increases the size of the actuator. With smaller two-cycle engines, this result was acceptable; however, the heavier four-cycle motors exacerbate this problem.
Moreover, the swivel and clamping brackets must be reinforced to handle the increased weight. The brackets also must be widened, which requires additional reinforcing, to accommodate the resulting larger sizes of the actuator, motor, reservoir and pump. Such reinforcing increases the size and weight of the brackets, as well as increases the manufacturing cost.
Prior powering units also include a valve that allows the outboard motor to be raised (i.e., tilted up) and lowered manually when the electric motor is not functioning. The valve, when open, places a chamber of the actuator in communication with the reservoir and/or with the opposite cylinder chamber in order to move the actuator by hand. This valve, however, commonly must be rotated with an aid of a tool, which makes actuation of the valve inconvenient. The tool also is often lost or misplaced by the watercraft owner.